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Latest IPCC report: human influence on climate confirmed

PETER LLOYD: The latest Intergovernmental Panel on Climate Change report virtually slams the gate on any doubt about the cause of climate change, arguing it is extremely likely that human influence has been the dominant cause of observed warming since the middle of last century.

The fifth IPCC report was released a short time ago in Stockholm.

It concludes it is virtually certain that there will be more frequent hot, few cold temperature extremes and more heatwaves over most land and sea areas.

Global sea levels will continue to rise, and the earth will continue to warm under all the IPCC's scenarios.

The ice sheets will continue to shrink.

The report suggests global temperatures will likely rise from between 1.5 degrees compared to 1850 and could exceed two degrees under certain scenarios.

The Assessment report compiles scientific knowledge on the physical evidence behind global warming. It was prepared by 600 contributing authors, 209 lead authors and 50 review editors from 32 countries.

One of the review editors is Professor Andy Pitman, the director of the ARC Centre of Excellence for Climate System Science at the University of New South Wales.

He's speaking to David Mark.

DAVID MARK: Professor Pitman, this is the fifth IPCC report, it says warming of the climate system is unequivocal. Each of these reports has got progressively stronger in terms of the likelihood that it's humans that are causing global warming. What does ‘extremely likely’ mean?

ANDY PITMAN: It means that there's something between a 95 and 100 per cent confidence in those statements, which in areas of science as complex as climate systems science is about as certain as you will ever get.

DAVID MARK: The report also says human influence on the climate system is clear, so is there any doubt that humans are causing climate change?

ANDY PITMAN: No, we're between 95 and 100 per cent certain that we can now detect human influence in warming on the atmosphere, on the oceans, on the global water cycle, on reductions in snow, in ice, in global sea level rise and in changes in many climate extremes - there isn't any doubt about that anymore.

DAVID MARK: The final wording of these documents can be quite political and as often changes right up to the last minute. You say there's between - there is no doubt, there's between a 95 and 100 per cent chance, why didn't the document come out, if you're so certain, you're one of the review editors and say there is a 100 per cent chance?

ANDY PITMAN: Because in science nothing is ever 100 per cent. Even something like relativity has some tiny elements of doubt associated with it and even something like evolution has some little tiny elements of doubt about it. Science isn't ever 100 per cent certain about anything, but once it gets above 90 or 95 per cent it's functionally certain and in any areas of decision-making that we might make as an Australian or world citizen, we never make decisions requiring 99 per cent certainty, we always make decisions with a lower probability of certainty than that and that should be now quite a common sight I think.

DAVID MARK: Okay well let’s look at what's new in this report compared to the previous report, the fourth that was released six years ago. What are the key headlines, what's changed?

ANDY PITMAN: Much more clear evidence around the warming patterns, much clearer evidence around sea level rise, in fact the sea level rise is likely higher than it was in the previous reports. Clearer evidence around particularly the trends in temperature extremes and clearer evidence around a number of other aspects and quite clearly a much clearer and more definitive set of statements around the human influence in those changes that have been observed.

DAVID MARK: You mentioned the temperature increases, what sort of scenarios are we looking at?

ANDY PITMAN: Well the good news is those scenarios are human dependant, so at the high end of emissions, the rates of emissions we're currently tracking, we're looking at warming of between about 2.6 and 4.8 degrees by the end of the century and those warming figures, something like 2.6 is equivalent of the change in global temperatures between an ice age and now, so we're talking about enormous temperature changes.

But the good news is if we can actually get emissions to the low range, the so-called RCP2.6, we might be able to keep global warming to below two degrees, which is threshold that governments have accepted as the threshold for dangerous climate change.

So there is a good news story in this report and that is if we can globally cut emissions very deeply and very quickly, we can still avoid two degrees of warming.

DAVID MARK: As you say that's very dependent on the amount of emissions, the amount of our global emissions. What needs to be done in order to achieve that best possible case scenario?

ANDY PITMAN: That's a very complex question, which we probably don't have time to go into the detail but as a back of the envelope rule of thumb, global emission cuts of about 3 per cent per year through to 2070 and negative emissions, that means removing Co2 from the atmosphere after about 2070.

DAVID MARK: So - and that would presume cutting begins right now?

ANDY PITMAN: That's right.

DAVID MARK: The report doesn't specifically mention Australia but perhaps you could extrapolate what sort of effects we might see in Australia looking at the various scenarios.

ANDY PITMAN: Well the sorts of countries that are vulnerable to the changes that are in the report tend to be the dryer continents, which obviously Australia is vulnerable to in that context. One of the more clear changes is an intensification of rainfall in the tropics and a reduction in rainfall in the areas that are already dry, implying they become drier. So I think just… we are expecting significant increases in temperatures over Australia and particularly temperature extremes over Australia, with an intensification in tropical rainfall and a reduction in rainfall away from the tropics.

DAVID MARK: This document is essentially an advisory document for governments. What message does it send to the governments around the world?

ANDY PITMAN: That the efforts made to date to cut global emissions of greenhouse gases aren't consistent with the science. The cut in greenhouse gas emissions have to be much deeper and much quicker than governments have so far taken on board.

DAVID MARK: Professor Andy Pitman, thanks very much for your time.

ANDY PITMAN: You're very welcome.

PETER LLOYD: That's David Mark talking to one of the review editors of the Climate Report, Professor Andy Pitman, the director of the ARC Centre of Excellence for Climate System Science at the University of New South Wales.

The headlines there - no doubt there is human influence on global warming but there is hope that the rise in global temperatures can be contained if there is global political will to act.